CONCLUSIONS
The results of this investigation show that it is possible to determine the concentration of hydrofluoric acid in hydrofluoric acid-water solutions by spectrophotometric measuremekt a t 1835 mp. Free hydrofluoric acid can be determined in aqueous hydrofluoric acid solutions, by a spectrophotometric method, in the presence of many metal complexes in equilibrium. Other acids in aqueous solutions can probably be determined in the same manner if only one acid is present and there are no other interfering substances. If several acids are present, then obviously total acid concentration would
be determined. This total acid concentration probably represents the concentration of hydronium ion in solution, although further proof of this is required. The ability to measure free hydrofluoric acid in complex aqueous solutions has resulted in the gain of important qualitative information about the ionic species present in tantalum-niobium-hydrofluoric acid solutions. The determination of free acid should be applicable to many other complex systems, making it possible to understand and control the degree of hydrolysis and, hence, types of ionic species in solution.
Metals Co. for permission to publish this paper. LITERATURE CITED
(1) Falk, M., Giguere, P. A., Can. J . C h . 35, 1195-204 (1957). (2) Jones, M. E., Rider, B. F., Hendrickson, H. C., General Electric Co., AEC
Reaearch and
Development XRpt.,
KAPL-1497 (1956). (3) Kanzelmeyer, J. H., Ryan, J., Freund, Harry, J . Am. C h . Soe. 78, 3020 (1956). (4) Werning, J. R., Higbie, K. B., Grace, J. T., Speece, B. F., Gilbert, H. L., Znd. Eng. Chem. 46, 644, 2491 (1954). (5) Wilhelm, H. A., Kerngan, J. U., U. S. Patent 2,767,047 (Oct. 16, 1956).
ACKNOWLEDGMENT
The authors thank the Union Carbide
RECEIVED for review May 14, 1959. Accepted August 14, 1959.
Spectrophotometric Determination of Antimony with Rhodamine B R. E. VAN AMAN, F. D. HOLLIBAUGH, and J. H. KANZELMEYER Zinc Smelting Division, St. Joseph Lead Co., Monaca, Pa.
b An
analytical procedure has been developed for the spectrophotometric determination of antimony in zinc metal and zinc oxide. Antimony(V) is extracted into isopropyl ether from a hydrochloric acid solution and a colored complex is formed with rhodamine B. The order of addition of reagents eliminates the hydrolysis of antimony(V), thus yielding more consistent results. Two to 20 y of antimony may be determined with a relative standard deviation of 1.2%.
R
appears to be the most specific and sensitive reagent available for the analysis of microgram quantities of antimony in zinc metal and zinc oxide. Previous methods involved a preliminary separation by extracting the hexachloroantimonate(V) from solutions containing less than 8N hydrochloric acid into an organic layer (4, 6, 7, 8). The color intensity depended on the length of time from dilution of the sample to the addition of the extracting medium, resulting in average errorsof lOto20% (%,S,S, l l , l % ) . The variability of these methods stemmed from the hydrolysis of antimonyfl) at the reduced hydrochloric acid concentration employed( 9 , l O ) . A procedure has been developed to eliminate this hydrolysis and a method is proposed, based upon this mode of operation, which haa a relative standard deviation of 1.2%. HODAMINE B
EXPERIMENTAL
Apparatus and Reagents. All absorbance measurements were made with a Beckman Model B spectrophotometer using 1-cm. borosilicate glass cells. Rhodamine B Solution (0.01% rhodamine B in 0.5N hydrochloric acid). Dissolve 0.1 gram of rhodamine B (National Aniline Division, Allied Chemical & Dye Corp.) in distilled water. Transfer to a I-liter flask containing 41.7 ml. of concentrated hydrochloric acid (36%) and dilute to volume with distilled water. HJ drochloric-Nitric Acid Mixture. Combine approximately 10 parts of hydrochloric acid with 1 part of nitric acid by volume. Standard Antimony Solution. Weigh 100 mg. of antimony metal (Baker & Adamson, reagent grade) and dissolve in about 15 ml. of the hydrochloricnitric acid mixture. Dilute to 100 ml. with concentrated hydrochloric acid. This solution contains 1 mg. of antimony per ml. Pipet 1.0 ml. of the above solution into a 200-ml. volumetric flask and dilute to volume with concentrated hydrochloric acid. This solution contains 5 y of antimony per ml. Procedure. Dissolve samples containing 5 to 20 7 of antimony in a minimum quantity of the hydrochloric-nitric scid mixture and add 1 ml. of concentrated sulfuric acid. Swirl vigorously until all the zinc is in solution. Evaporate to Rtrong fumes of sulfur trioxide, cool to room ternperature, and add 10 ml. of concentrated hydrochloric acid to dissolve
the precipitated salts. Transfer to 125-ml. Beparatory funnels, rinse beakers with 7 ml. of concentrated bydrochloric acid, and combine with samples. Add, by pipet, 15.0 ml. of isopropyl ether, stopper, and shake for 30 seconds. Add 7 ml. of distilled water and mix immediately. Cool in a water bath (25" C.) for 10 minutes and shake for 30 seconds. After separation of the organic and aqueous layers, discard the lower (aqueous) layer. Add 20 ml. of the rhodamine B solution and shake for 30 seconds. Again discard the lower (aqueous) layer. Transfer the ether layer to 15ml. centrifuge tubes and decant into l-cm. absorption cells. (This transfer eliminates water droplets in the absorption cells.) Read the absorbance at 550 mp against a water blank as soon as the samples are transferred to the cells to prevent change of concentration due to solvent evaporation. Prepare a standard curve from samples containing the same quantity of zinc (J. T. Baker Chemical Co., ACS specifications) as the samples to be analyzed. Add 1, 2, 3, 4, and 5 ml. of the standard antimony solution (5 y of antimony per ml.) and run through the entire procedure. Plot the absorbance values a t 5, 'IO, 15, 20, and 25 y of antimony, respectively. Modify the procedure for the analysis of zinc oxide by taking the sample into solution with 10 ml. of concentrated hydrochloric acid. Use 7 ml. of hydrochloric acid to rinse the samples into the separatory funnels. Add 2 mg. of ceric sulfate, and follow the procedure beginning a t the step in which isopropyl ether is added. V O L 31,
NO. 11, NOVEMBER 1959
1783
Samples containing metallic zinc must be dissolved with an oxidizing acid mixture to prevent loss of antimony as gaseous stibine. Only hydrochloric acid is needed for nonmetallic samples, which eliminates the necessity of fuming with sulfuric acid. I n the latter case, however, the addition of ceric sulfate is required to ensure that all of the antimony is converted to its highest oxidstion state. Contrary to previous reports (IO), no difficulty is encountered with the small excess of ceric ion remaining in solution and it was deemed unnecessary to add hydroxylamine hydrochloride to reduce it. Considerable care must be exercised in the evaporation of the hydrochloricnitric-sulfuric acid mixture to fumes of sulfur trioxide. If this is carried out too rapidly and at too high a temperature, loss of antimony chloride results. The hydrochloric acid concentration obtained by following the given procedure is 8 N . Any convenient concentration from 3 to 8 N may be used with equal success. A small blank (0.01 to 0.02 absorbance unit) was obtained when antimony-free metal was run by the procedure. More reproducible results were obtained, however, by using distilled water as a blank for all standards and samples. Zinc depresses the absorbance about 7.5% per gram. Therefore, different sample sizes require separate standard curves. Absorbance is a linear function of antimony concentration up to 20 y. The molar absorptivity obtained for samples containing 0.2 gram of zinc was 128,000 liter mole-' cm.-1. The antimony-rhodamine B complex in isopropyl ether is relatively stable, fading only 1.2% in 1.5 hours. However, after 18 hours, 30% of the original absorbance is lost. DISCUSSION
Hydrolysis. The extent of hydrolysis was determined by preparing
Table I.
Elemcnt As
cu
Amount,, 7 10 100
Figure 1. HFect of addition order of water
'I
I WL.",.,
100 500 100 600
of SOa.
1784
ANALYTICAL CHEMISTRY
I
Figure 2. Effect of HCI Concentration during extraction Ether added prior to water
0 Water added prior to ether
samples containing 15 7 of antimony and running them through the procedure, allowing various times of hydrolysis before extraction and color development. The first set was carried out in the manner previously used-the antimony(V) was obtained in Concentrated hydrochloric acid and diluted t o 8 N . Isopropyl ether was added after a measured time interval, the samples shaken, and the color developed. The absorbance plotted us. the time of hydrolysis is shown as the solid line in Figure 1. A second set of samples (dotted line in Figure 1) containing the same amount of antimony, was obtained in concentrated hydrochloric acid. Isopropyl ether was added prior to dilution of the aqueous phase to 8 N . After a measured time interval, the aqueous layer was discarded and the color developed. No decrease in absorbance was noted in any of the sam-
Interference of Elements
Source Material A szOa
% 0.005 0.05 0.05 0.25 0.05
Metal SnC12 Metal Metal Metal 0.30 NOz100 KNOa 0.05 In 125 Metal 0.062 TI 100 TlNOs 0.05 Mn 50 KMnO, 0.025 Cd 2000 Metal 1.0 Pb 2000 Metal 1.0 NO3 Large excess" HNOa ... Sample taken into solution with HC1, "08, and HzSO,, and Sn .41 Ge Fe
7 01 "CL
Effect on Antimony Determination None None None None None None None None High results None None None Color fades not evaporated to fumes
ples, indicating that hydrolysis had been effectively eliminated. Hydrochloric Acid Concentration for Extraction. According t o Edwards and Voigt ( I ) , antimony(V) extracts to the extent of 99.5% into isopropyl ether from aqueous solutions 6.5 t o 8.5N in hydrochloric acid. The variation in extraction as a furdion of hydrochloric acid concentration was studied in a manner analogous to that outlined in the previous section These data are shown in Figure 2. I:r the proposed procedure, the acidity may be varied from 3 to 8 N without scrious change in the sensitivity of the method, although i t should be mairitaiced at the selected level for all samp'-s. Effect of Rhoaamine B Concentration. Concentrations of rhodamine B from 0.001 t o u . l % were tried in t h e color development, Lower concentrations yielded decreased absorbance. Difficulty with solubility was experienced with high concentrations. T h e optimum rhndamine B concentration was 0.01%. The rhodamine B solution was made 0.5N in hydrochloric acid to eliminate a precipitate which otherwise occasionally occurred. Interferences. The interference of selected elements has been studied by adding known amounts of these elements to samples containing 15 7 of antimony and noting a n y variation from the expected absorbance. The results are tabulated in Table I. Gold, gallium, mercury, and silverthe other elements known t o extract into organic solvents with rhodamine B-were not investigated because they are not normally present in zinc or zinc oxide in significant amounts. Thallium extraction is nearly complete under the conditions given in the procedure. If thallium is present, it may be separated by extraction from IN hydrobromic acid into isopropyl ether. The antimony will remain in the aqueous layer and may be determined by evaporating to a small volume on a steam bath, adding concentrated hydrochloric acid, and carrying out the procedure. Alternatively, the antimony may be measured by the difference between the absorbance due to antimony plus thallium (no separation) and the absorbance due to thallium alone. Accuracy. The accuracy of the method was determined by adding known amounts of antimony t o 0.2-
gram samples of National Bureau of Standards zinc spelter No. 108 which contains 0.0003% antimony. Results are shown in Table 11.
Table II. Antimony Determination on Zinc Metal
Voigt, A . F., ANAL. 21, 1204-5 (1949).
Segriwe, E., 2. anal. C h m . 70, 400 327).
(uznetsov, V. I., C o n p t . rend. mud. 946).
CHEW 25, 674 (1953): (5) Luke, C. L., Campbell, M. E., Zbid., 25, 1592 (1953). (6) Maren, T. H., Zbid., 19, 487-91 (1947). . .
Extraction in Analytical Chemistry,” p. 154, Wiley, New York, 1957. (9) Neumann, H. M., J . Am. Chem. SOC. 76, 2611 (1954).
LITERATURE CITED (EM.
(7) Milner, G. W. C., Analyst 81, 622-3 (1956). (8) Marriaon, G. H., Freiser, H., “Solvent
5 5 5 15 15 15
4.90 5.05 5.00 14.90 15.19 15.09
Est. std. dev.
-2.00 +1.W 0.00 -0.67 +1.27 +0.60
1.21
(lO).Ramette, R. W., Sandell, E. B., Anal. Chim. Acta 13, 455-8 (1955). ( 1 1 ) . Sandell, E. B., “Colorimetric Deterrmnation of Traces of Metals,” pp. 16374, Interscicnce, New York, 1950. (12) White, C. E., Rose, H. J., ?INAL. CHEM.25, 351-2 (1953). RECEIVEDfor review May 13, 1959. Accepted August 6, 1959. Division of Analytical Chemistry, 135th Meeting, ACS, Boston, Mass., April 1959.
Determination of Gamma-Ray Abundance Directly from the Total Absorption Peak D. F. COVELL
U . S. Naval Radiological Defense Laboratory, San Francisco 24, Calif. b Gamma-ray activity i s determined by using data obtained from scintillation spectrometer pulse height distributions. The digital data contained in that part of the distribution known as the total absorption peak are analyzed directly, and a statistical evaluation of the precision of the method i s presented. Methods for quantitative interpretation of y-ray pulse analysis data, where discrete y-rays are being observed, have usually involved some form of graphical reduction. The subjectivity inherent in the preparation and interpretation of the graphic form, however, sacrifices precision. Greater precision i s realized by taking advantage of the digital nature of pulse height distribution data and applying statistical methods of reduction. The method i s applicable to radiochemical analysis.
I
Mn54
PULSE
T
HE technique of y-ray measurement by pulse height analysis has been used to supplement qualitative radiochemical analytical procedures and has made possible very rapid and positive qualitative identification of radionuclides. The technique more recently has been extended t o the quantitative determination of radionuclide abundances (3). By combining this and conventional analytical procedures according to the requirements of particular problems, i t is possible to realize significant benefits in speed, simplicity, accuracy, and precision in making such determinations. The method reported here for interpretation of pulse height distribution data takes advantage of the
Figure 1.
H E I G H T
-
Typical pulse height distributions of pure radionuclides
digital nature of the data and permits direct quantitative evaluation. THEORY
Pulse Height Distribution Curve. Gamma-ray pulse height distributions have forms typical of those shown in Figure 1, where the ordinate represents counts per pulse height increment and the abscissa represents pulse height. These are distributions for pure specimens of tin-113, cesium137, manganese-54, and zinc-65, having principal y-ray energies of 260,
662, and 840 k.e.v., and 1.12 m.e.v., respectively. I n each case the distribution consists of a prominent, well defined, approximately Gaussian-shaped region referred to as the total absorption peak and a region of nonunique appearance. The physical phenomena which take place in the detection and measurement apparatus to produce the particular shapes which these distributions have are described elsewhere ( 1 ) . The characteristics of the distribution which are of interest here may be summarized as follows: VOL. 31,
NO. 1 1, NOVEMBER 1959
1785
